Originally Posted by
weavers
they don't have 18-25?
Various tube manufacturers label their tubes differently. A tube that is labeled as 18-25 doesn't have any magical properties that allows for a greater range than two different tubes labeled as 18-23 or 23-25. I think it's pretty smart for tube makers to generalize a little, because it means that they don't have to make two slightly different sized tubes.
In general, tubes marked as 18-23 work in pretty much everything up to a 30 mm width or so tire. They will be thinner in a larger tire, and in theory more prone to punctures, but they work fine.